Means for preventing contact sticking in mercury contact switches



Jan. 23, 1962 C. E. POLLARD, MEANS FOR PREVENTING CONTAC JR T STICKINGIN MERCURY CONTACT SWITCHES Filed Oct. 22, 1959 //v l/ENTOR C. E. POLLARO, JR.

ATTORNEY United Stes This invention relates to electric switches andparticularly to such switches in which metallic material in liquid formis used as a medium through which circuit contina ty is effected.

Switches of the kind under consideration are often called mercuryswitches because of the common use of this material as the liquidcontact medium. Although a mercury switch may take several forms, thereis disclosed for illustrative purposes one of the mercury contact typeas in Patents 2,609,464 to J. T. L. Brown and C. E. Pollard, Jr.and"2,868,926 to C. E. Pollard, Jr.

It has been previously discovered, as set forth in Patent 2,732,459 toC. E. Pollard, Jr., that in switches having mercury as the contactmedium, the contacts have a tendency to stick. One solution of thesticking problem is set forth in this last noted patent, namely, the useof a copper-mercury solution in place of mercury alone where allcontacts are substantially platinum.

It is an object of this invention to further improve the structure andthus the operation of mercury type contact switches in which the wettedcontacts tend to stick where one or more of the contacts are nickel or asimilar metal.

This object is attained in accordance with a feature of this inventionby using a solution of mercury, copper and tin as the contact medium.

The foregoing and other objects and features of this invention willappear more fully and clearly from the ensuing description of a switchstructure illustrated in the appended drawing in which the single figureshows in partial section an electromagnetically operable sealed reedswitch having as a contact medium a solution of mercury, copper and tin.

The reed switch illustrated comprises an envelope or housing 10, whichmay be of glass. In one end a of the envelope 10, spaced pole-pieceterminals 11 and 12 of magnetic material are sealed. The facing innerends of the terminals 11 and 12 are provided with contacts 13 and 14,respectively, which may be of platinum or platinum and nickel.

The opposite end 10b of the envelope 10 has a metal tube 20 extendingthrough and sealed therein. A part of the tube within the envelope has aflared or cup-like portion 20a. Contained within this cup portion anddesignated 21 is a quantity of the mercury-copper-tin solutionpreviously noted. There may be an excess of this solution surroundingthe cup.

A reed or swinger of magnetic material, such as Permalloy, is secured tothe cup a as at 15a and has a looped portion 15b within the cup. Thereed 15 may atent O 3,018,354 Patented Jan. 23, 1962 ICC beadvantageously coated with nickel to improve its mercury wettability.

An energizing coil 22, shown schematically in the drawing, surrounds theenvelope 10.

The theory of operation of mercury contact switches is known to thoseskilled in the art and is, accordingly, not here discussed. For furtherinformation with regard to the particular type of switch chosen toillustrate this invention, reference is made to the previously notedPatents 2,609,464 and 2,868,926.

The liquid contact medium may comprise the mercury, tin and copper invarious proportions. For example, suitable nonsticking contacts havebeen made with 6.0 milligrams of tin and 0.3 milligram of copper in 0.1cubic centimeter of mercury. The lower limit of copper useful for theintended purpose is not clearly defined, although 0.25 milligram of tinand 0.3 milligram of copper in 0.1 cubic centimeter of mercury attainedthe desired result. The upper limit for copper appears to be 0.05percent and that for tin about 0.5 percent by weight. The lower limitfor tin appears to be about 0.01 percent by weight.

Thus, one may use the maximum amount of tin and of copper or less ofeither or both down to a minimum beyond which the desired effect is notachieved. In view of the much greater amount of tin than copper that maybe dissolved in mercury and of its apparently greater effect on thecontact operation, the minimum of copper may be none at all providedsufficient tin is used.

Although this invention has been disclosed with respect to a particularswitch illustrative thereof, it is not confined to such structure butmay be used advantageously in other liquid contact switches subject tocontact sticking.

What is claimed is:

1. In an electric switch of the type employing engageable wettedcontacts, an agent for wetting the con tacts comprising amercury-tin-copper solution.

2. In an electric switch of the type employing engageable wettedcontacts, at least one of which is nickel, an agent for wetting thecontacts comprising a mercury-tincopper solution.

3. In an electric switch having engageable contacts housed in aninsulating envelope, liquid mercury with tin and copper dissolvedtherein.

4. An electric switch having movable circuit controlling elemenrtshoused in a sealed insulating envelope, and a pool of mercury-tin-coppersolution in said envelope.

5. An electric switch in which circuit continuity is maintained by wayof contacts wetted by a liquid contact material comprising tin in anamount up to 0.5 percent by weight and copper in an amount up to 0.05percent by weight dissolved in mercury.

References Cited in the file of this patent UNITED STATES PATENTS2,319,259 Peterson May 18, 1943 2,732,459 Pollard Jan. 24, 1956.2,796,495 Keitel et a1. June 18, 1957,

1. IN AN ELECTRIC SWITCH OF THE TYPE EMPLOYING ENGAGEABLE WETTEDCONTACTS, AN AGENT FOR WETTING THE CONTACTS COMPRISING AMERCURY-TIN-COPPER SOLUTION.